Factory Aux battery not charging

[mikracer]

So I bought my van 9 years ago (to the day actually!) and I am just now getting to replacing the factory frame mounted auxiliary battery. The battery wasn't charging so I replaced the solenoid under the starter battery tray. I checked to see if it was charging and it showed 14v the first day. I didn't think anything of it after that but I went to hook up my toy hauler and the rear battery was dead again and not charging.

I replaced the battery today and checked the various maxi fuses under the hood as well as some of the fuses in the cabin. I replaced one 15amp fuse, but it is still not getting charge. I then replaced the solenoid again to see if that was the problem, but no luck. I'm seeing if anyone else can offer some advice. I am attaching a couple pages from the Ford wiring manual to show what I'm working with.

The solenoid has 2 main lugs. Does it matter which side the wires go? On one side I have the red wire and on the other side I have the white/violet and red/yellow. There is also a small wire that goes onto a smaller lug in the middle.

The only thing I haven't replaced at this point is the trailer tow relay that's located in the fuse box under the hood.

[dhally]

There is a mini relay in one of the fuse boxes that disconnects the aux battery when the ignition is off. It is in the diagram.

[mikracer]

Originally Posted by dhally

There is a mini relay in one of the fuse boxes that disconnects the aux battery when the ignition is off. It is in the diagram.

I just tested the relay and it appears to be working correctly.

I'm wondering if my wiring at the solenoid is the problem. Can anyone confirm which wires go on which lug of the solenoid? Right now I have the red and red/yellow wire on one side and the white/violet on the other.

[Scalf77]

For the most part the solenoid doesn't care. But the wh/vt larger wire should always be hot, you can check with a volt meter. The red/yellow and red ( which is probably not factory) can go on the other side. It says you also have another smaller wht/vt going to the coil, this should be 12 volts when the van is running. The ground for the coil is the connection of the solenoid to the body of the van. So make sure that is a clean connection. You should be able to use case of solenoid as your ground connection. If your not reading 12 volts for either of the 12 volt connections it could be grounded poorly.

The red yellow should have 12 volts when running, if not work backwards.

-greg

[mikracer]

Hi Scalf,

Thank you for your reply! All the wiring is factory. The solid red wire is the hot wire to the aux battery. Testing that lug shows the same volts as the aux battery.

I'll have to double check the other wires. One of them got voltage when the key was on, but the other never got voltage.

One other thing is when I was testing everything yesterday, I didn't have it bolted back down so that could have been my problem as well.

Thanks again for the info and I'll post back once I get some time to tackle it again.

Originally Posted by Scalf77

For the most part the solenoid d
oesn't care. But the wh/vt larger wire should always be hot, you can check with a volt meter. The red/yellow and red ( which is probably not factory) can go on the other side. It says you also have another smaller wht/vt going to the coil, this should be 12 volts when the van is running. The ground for the coil is the connection of the solenoid to the body of the van. So make sure that is a clean connection. You should be able to use case of solenoid as your ground connection. If your not reading 12 volts for either of the 12 volt connections it could be grounded poorly.

The red yellow should have 12 volts when running, if not work backwards.

-greg

[mikracer]

With the help of Scalf77, I was able to isolate the issue and finally get the aux battery charging as it should.

With the two replacement solenoids I had, the 15 amp fuse in slot #22 the cabin fuse panel kept blowing the instant I turned the key to "on". Testing the resistance from the charge coil to the body of the solenoid ultimately led to the discovery of the failed solenoids. I finally got a good solenoid that passed the bench test and once installed, the aux battery was finally charging.

Feels good to get something working that hasn't worked for 9 years...